UK light-heavyweight Joshua Buatsi earned a win yet unimpressive beginning to life under recent management with a points victory over Parker in the Manchester arena.
The Olympic medal winner's work rate seemingly secured him a judges' verdict in a competitive 10-round bout at the Manchester venue.
But Parker had his moments, delivering effective single shots in a match where the techniques didn't complement each other, with frequent clinching spoiling the fight.
The scoring judges judged it 96-94 in favor to Buatsi, with the final judge a even score.
"It wasn't my best display but how do champions respond? They win," the victor said in the ring as he was faced negative reactions from the crowd.
The Londoner got back to winning after his maiden career setback - an thrilling contest with his previous opponent in last winter - to earn a 20th career victory.
Some ringside observers felt the challenger, thirty-one, should have been awarded the decision but the contender endured the second setback of his 28-fight career.
Buatsi Earns Win in Uneventful Encounter
The fighter's advancement has plateaued in recent years through promotional disputes and long spells of lack of fights.
Earlier forecast as the next star of the British fight scene, he now finds himself trying to achieve expectations - possibly in what feels like a final roll of the dice - under fresh management.
He began cautiously, with neither fighter prepared to overcommit in a calculated early stages.
Parker, whose only previous defeat came at super middleweight against his former opponent in two years ago after damaging his hand during the bout, was participating in his second fight at the higher weight class.
By the fight's midpoint, the underdog had kept it close, causing problems for the favorite, who utilized a tight guard to edge the cleaner periods.
The crowd's patience decreased during regular grabbing, with the challenger falling to the floor various instances during close exchanges.
Parker finished the stronger, but several stanzas were challenging to assess. Nevertheless, previous titleholder the boxing analyst - commentating on the broadcast network - had it strongly leaning for the challenger, scoring for Buatsi just a single round.
The victor progresses, but with the presence of hard hitter David Benavidez, and Russian star Bivol dominating the weight class, the path to championship success - judging by this showing - still looks steep.
Ricky Hatton Tribute Fuels Local Rivalry Battle
In the co-main event, Lyndon Arthur overcame Rea by divided decision in a excellent Manchester vs Manchester contest to secure the continental belt.
The stadium grew hushed for a extremely emotional tribute before the fight as 10 bells sounded in honor of local hero Ricky Hatton, who passed away aged 46 in last month.
It was the premier televised fight night in the city since the passing of Hatton. As the concluding sound faded, the stillness gave way to a chant of "there's just one Ricky Hatton".
The fighting inside the ropes matched the sentiment. Arthur was floored by a left hook squarely on the jaw in the initial stage, rising shakily to his position on the eight count.
But the Manchester United-red shorts of the fighter soon advanced again. From the other corner, the opponent - in rival City blue - was marked up soon, significant bruising appearing under his face as the fighters landed powerful shots.
The challenger, 27, delivered effective strikes but Arthur, 34, matched the intensity with effective uppercuts as the intensity hardly diminished over the full distance.
The victor barely secured the decision with judges scorecards of draw, close margin and wider gap, but the two athletes were determined and full of heart, everything their inspiration the legend embodied.
